From b0ec8525aab51fea854d1e71c971244deeab7d83 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Fri, 1 Sep 2023 12:40:51 +0200
Subject: [PATCH] Add support for editing `WheeledVehicle` wheels config at
 runtime without full physics state rebuild

#1324
---
 .../Engine/Physics/Actors/WheeledVehicle.cpp  | 25 ++++++++++
 .../Physics/PhysX/PhysicsBackendPhysX.cpp     | 47 +++++++++++++++++++
 Source/Engine/Physics/PhysicsBackend.h        |  1 +
 Source/Engine/Physics/PhysicsBackendEmpty.cpp |  4 ++
 4 files changed, 77 insertions(+)

diff --git a/Source/Engine/Physics/Actors/WheeledVehicle.cpp b/Source/Engine/Physics/Actors/WheeledVehicle.cpp
index f5f729d39..0ab8e6518 100644
--- a/Source/Engine/Physics/Actors/WheeledVehicle.cpp
+++ b/Source/Engine/Physics/Actors/WheeledVehicle.cpp
@@ -40,6 +40,31 @@ const Array<WheeledVehicle::Wheel>& WheeledVehicle::GetWheels() const
 
 void WheeledVehicle::SetWheels(const Array<Wheel>& value)
 {
+#if WITH_VEHICLE
+    // Don't recreate whole vehicle when some wheel properties are only changed (eg. suspension)
+    if (_actor && _vehicle && _wheels.Count() == value.Count() && _wheelsData.Count() == value.Count())
+    {
+        bool softUpdate = true;
+        for (int32 wheelIndex = 0; wheelIndex < value.Count(); wheelIndex++)
+        {
+            auto& oldWheel = _wheels.Get()[wheelIndex];
+            auto& newWheel = value.Get()[wheelIndex];
+            if (oldWheel.Type != newWheel.Type ||
+                Math::NotNearEqual(oldWheel.SuspensionForceOffset, newWheel.SuspensionForceOffset) ||
+                oldWheel.Collider != newWheel.Collider)
+            {
+                softUpdate = false;
+                break;
+            }
+        }
+        if (softUpdate)
+        {
+            _wheels = value;
+            PhysicsBackend::UpdateVehicleWheels(this);
+            return;
+        }
+    }
+#endif
     _wheels = value;
     Setup();
 }
diff --git a/Source/Engine/Physics/PhysX/PhysicsBackendPhysX.cpp b/Source/Engine/Physics/PhysX/PhysicsBackendPhysX.cpp
index 4b18804da..619f025ed 100644
--- a/Source/Engine/Physics/PhysX/PhysicsBackendPhysX.cpp
+++ b/Source/Engine/Physics/PhysX/PhysicsBackendPhysX.cpp
@@ -2923,6 +2923,53 @@ void PhysicsBackend::DestroyVehicle(void* vehicle, int32 driveType)
     }
 }
 
+void PhysicsBackend::UpdateVehicleWheels(WheeledVehicle* actor)
+{
+    auto drive = (PxVehicleWheels*)actor->_vehicle;
+    PxVehicleWheelsSimData* wheelsSimData = &drive->mWheelsSimData;
+    for (uint32 i = 0; i < wheelsSimData->getNbWheels(); i++)
+    {
+        auto& wheel = actor->_wheels[i];
+
+        // Update suspension data
+        PxVehicleSuspensionData suspensionData = wheelsSimData->getSuspensionData(i);
+        const float suspensionFrequency = 7.0f;
+        suspensionData.mMaxCompression = wheel.SuspensionMaxRaise;
+        suspensionData.mMaxDroop = wheel.SuspensionMaxDrop;
+        suspensionData.mSpringStrength = Math::Square(suspensionFrequency) * suspensionData.mSprungMass;
+        suspensionData.mSpringDamperRate = wheel.SuspensionDampingRate * 2.0f * Math::Sqrt(suspensionData.mSpringStrength * suspensionData.mSprungMass);
+        wheelsSimData->setSuspensionData(i, suspensionData);
+
+        // Update tire data
+        PxVehicleTireData tire;
+        int32 tireIndex = WheelTireTypes.Find(wheel.TireFrictionScale);
+        if (tireIndex == -1)
+        {
+            // New tire type
+            tireIndex = WheelTireTypes.Count();
+            WheelTireTypes.Add(wheel.TireFrictionScale);
+            WheelTireFrictionsDirty = true;
+        }
+        tire.mType = tireIndex;
+        tire.mLatStiffX = wheel.TireLateralMax;
+        tire.mLatStiffY = wheel.TireLateralStiffness;
+        tire.mLongitudinalStiffnessPerUnitGravity = wheel.TireLongitudinalStiffness;
+        wheelsSimData->setTireData(i, tire);
+
+        // Update wheel data
+        PxVehicleWheelData wheelData;
+        wheelData.mMass = wheel.Mass;
+        wheelData.mRadius = wheel.Radius;
+        wheelData.mWidth = wheel.Width;
+        wheelData.mMOI = 0.5f * wheelData.mMass * Math::Square(wheelData.mRadius);
+        wheelData.mDampingRate = M2ToCm2(wheel.DampingRate);
+        wheelData.mMaxSteer = wheel.MaxSteerAngle * DegreesToRadians;
+        wheelData.mMaxBrakeTorque = M2ToCm2(wheel.MaxBrakeTorque);
+        wheelData.mMaxHandBrakeTorque = M2ToCm2(wheel.MaxHandBrakeTorque);
+        wheelsSimData->setWheelData(i, wheelData);
+    }
+}
+
 void PhysicsBackend::SetVehicleGearbox(void* vehicle, const void* value)
 {
     auto drive = (PxVehicleDrive*)vehicle;
diff --git a/Source/Engine/Physics/PhysicsBackend.h b/Source/Engine/Physics/PhysicsBackend.h
index f72c7f679..ba452cda7 100644
--- a/Source/Engine/Physics/PhysicsBackend.h
+++ b/Source/Engine/Physics/PhysicsBackend.h
@@ -245,6 +245,7 @@ public:
     // Vehicles
     static void* CreateVehicle(class WheeledVehicle* actor);
     static void DestroyVehicle(void* vehicle, int32 driveType);
+    static void UpdateVehicleWheels(WheeledVehicle* actor);
     static void SetVehicleGearbox(void* vehicle, const void* value);
     static int32 GetVehicleTargetGear(void* vehicle);
     static void SetVehicleTargetGear(void* vehicle, int32 value);
diff --git a/Source/Engine/Physics/PhysicsBackendEmpty.cpp b/Source/Engine/Physics/PhysicsBackendEmpty.cpp
index 516562e28..28d849a32 100644
--- a/Source/Engine/Physics/PhysicsBackendEmpty.cpp
+++ b/Source/Engine/Physics/PhysicsBackendEmpty.cpp
@@ -732,6 +732,10 @@ void PhysicsBackend::DestroyVehicle(void* vehicle, int32 driveType)
 {
 }
 
+void PhysicsBackend::UpdateVehicleWheels(WheeledVehicle* actor)
+{
+}
+
 void PhysicsBackend::SetVehicleGearbox(void* vehicle, const void* value)
 {
 }